Pomegranate peel as a natural reducing agent in leaching of manganese concentrate

The present study explores, for the first time, the potential of pomegranate peel as a reductant agent for the reductive leaching of manganese concentrate, where pyrolusite is the primary valuable mineral. Furthermore, the influence of several factors on the reductive leaching process, including agitation speed, sulfuric acid concentration, peel quantity, reaction temperature and time were investigated. Under optimized conditions of 1.5 M sulfuric acid, temperature of 75 °C, agitation speed of 450 rpm, reaction time of 4 h and pomegranate peel quantity of 5 g, the recovery of dissolved manganese reached 96.12%. Scanning electron microscopy of the leaching residue revealed the dissolution of pyrolusite. Fourier-transform infrared spectroscopy analysis was conducted on both the pomegranate peel and the leaching residue to identify changes in functional groups. Additionally, the kinetics of the reductive leaching process were examined, indicating that the reaction rate is controlled by a surface chemical reaction mechanism with an activation energy of 38.39 kJ/mol. The enthalpy and entropy changes of the reaction were determined to be 35.71 kJ/mol and 192.90 J/mol·K, respectively. Based on thermodynamic values, the Gibbs free energy at temperatures of 303, 318, 333 and 348 K was found to be 94.16, 97.05, 99.95 and 102.84 kJ/mol, respectively.